Old 07-15-2019, 08:44 PM   #1
Fritz
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Default Microphone T-powering question

I'm planning to use the attached diagram to put t-power in a channel of an XLR patchbay using a 12v battery pack for an old Microtech Gefell PM860 mic. MY question is to make sure I'm not going to mess up a modern preamp running 12v across pins 2 and 3 with nothing to ground.

Thanks
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Old 07-16-2019, 04:16 AM   #2
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That's about what you need. Should work with any mixer, but I'd stay away from mixers with transformers on the input, as it will magnetise the transformer core, resulting in noise later on.
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Old 07-16-2019, 03:11 PM   #3
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Thank you sir
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Old 07-21-2019, 12:23 PM   #4
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Quote:
Originally Posted by Fritz View Post
I'm planning to use the attached diagram to put t-power in a channel of an XLR patchbay using a 12v battery pack for an old Microtech Gefell PM860 mic. MY question is to make sure I'm not going to mess up a modern preamp running 12v across pins 2 and 3 with nothing to ground.

Thanks

You need to make sure that there is(are) input capacitors on the feed to the pre amp, most pre amps will have these but check because if not , and the input is transformer balanced, you will probably blow the T power supply.
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Old 08-02-2019, 12:59 PM   #5
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Sorry I missed it for so long. After looking inside the n691 supply and finding the schematic I discovered that these gefells have their own powering scheme so I am replacing the circuit with a battery inside the supply box.

The circuit is 2 independent 12v supplies going to pin 4 on each of the microphone tuchell inputs. All the rest of the pins just parallel the inputs and outputs but the 12v only goes to the microphones.

With T-powering the 12v goes to + and - signal wires through 180 ohm resistors on each. The Gefell n691 sends the 12v positive through pin 4 on the tuchell which is dedicated for this power and the negative to ground.

Hopefully I have this right corrections are welcome
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Last edited by Fritz; 08-02-2019 at 01:27 PM.
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Old 08-02-2019, 05:29 PM   #6
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I was getting 13.2 volts out of the 12v battery pack, 8 AA battery pack duh, so I put a 180 ohm resistor between the battery positive and the mic power pin 4 and with the mic hooked up now it's at 12.5 volts. I figured that's close enough. It works! I even managed to use the existing power switch.
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